U.S. Defense Secretary Leon Panetta walks off his plane as he arrives at Kabul International Airport in Kabul, Afghanistan Thursday, June 7, 2012. Panetta arrived in Afghanistan on Thursday to take stock of progress in the war and discuss plans for the troop drawdown, even as violence spiked in the south. (AP Photo/Jim Watson, Pool)

U.S. Defense Secretary Leon Panetta walks off his plane as he arrives at Kabul International Airport in Kabul, Afghanistan Thursday, June 7, 2012. Panetta arrived in Afghanistan on Thursday to take stock of

Traders Gordon Charlop, left, and Kevin Lodewick work on the floor of the New York Stock Exchange, Thursday, Oct. 2, 2014. U.S. markets were mostly flat in early trading Thursday, follow a sell-off the day before, as U.S. investors had little reaction to comments from European Central Bank President Mario Draghi, who announced new economic stimulus measures for the continent. (AP Photo/Richard Drew)

Traders Gordon Charlop, left, and Kevin Lodewick work on the floor of the New York Stock Exchange, Thursday, Oct. 2, 2014. U.S. markets were mostly flat in early trading Thursday, follow a sell-off the day

U.S. Defense Secretary Leon Panetta, center right, speaks with U.S. Ambassador to Afghanistan Ryan Crocker, second right, and the head of NATO coalition forces in Afghanistan Gen. John Allen, center left, upon his arrival at Kabul International Airport in Kabul, Afghanistan Thursday, June 7, 2012. Panetta arrived in Afghanistan on Thursday to take stock of progress in the war and discuss plans for the troop drawdown, even as violence spiked in the south. (AP Photo/Jim Watson, Pool)

U.S. Defense Secretary Leon Panetta, center right, speaks with U.S. Ambassador to Afghanistan Ryan Crocker, second right, and the head of NATO coalition forces in Afghanistan Gen. John Allen, center left, upon

KABUL, Afghanistan (AP) -- U.S. Defense Secretary Leon Panetta on Thursday pressured Pakistan to do more to root out the al-Qaida-linked Haqqani terrorist network, saying American officials are "reaching the limits of our patience."

At a news conference in neighboring Afghanistan, Panetta repeatedly emphasized U.S. frustration with attackers crossing the border from Pakistan. It's essential that Pakistan stop "allowing terrorists to use their country as a safety net in order to conduct their attacks on our forces," he said alongside Afghan Defense Minister Abdul Rahim Wardak.

"We have made that very clear time and time again and we will continue to do that, but as I said, we are reaching the limits of our patience," Panetta said.

Panetta's explicit and repeated criticism of Pakistan's inaction, which he also voiced in his visit to India, appeared to signal a somewhat tougher stance and a suggestion that the U.S. is becoming even more willing and quick to strike terrorist targets inside Pakistan. A senior U.S. official acknowledged Thursday that the recent increase in drone strikes on insurgents in Pakistan is due in part to frustration with Islamabad. The official spoke on condition of anonymity to discuss sensitive operations.

The Haqqani group has been blamed for several attacks on Americans in Afghanistan, including last year' assault against the U.S. Embassy and NATO headquarters with rocket-propelled grenades. The group, which also has ties to the Taliban, has emerged as perhaps the biggest threat to stability in Afghanistan.

U.S. lawmakers from both parties have been urging the State Department to designate the Haqqani network a foreign terrorist organization.

The United States has given Pakistan billions of dollars in aid for its support in fighting Islamist militants. Despite pressure from the U.S., Pakistan has remained reluctant to go after insurgents, particularly the Haqqani network.

"It is an increasing concern that the safe haven exists and that there are those -- likely Haqqanis -- who are making use of that to attack our forces," Panetta said in his second day of blunt criticism of Pakistan.

For more than three decades the Haqqani network, led by the elderly Jalaluddin Haqqani, has maintained headquarters in Pakistan's Miran Shah district of North Waziristan. Pakistan has denied aiding the Haqqanis, and the Pakistani military has refused to carry out an offensive in the North Waziristan tribal region, saying it would unleash a tribal-wide war that Pakistan could not contain.

Panetta said the U.S. continues to see Haqqani fighters moving from Pakistan into Afghanistan to attack American forces -- most recently on June 1 when he said they detonated a truck bomb and then tried to storm Forward Operating Base Salerno in Khost province. Some U.S. service members were wounded in the attack, which was repelled by coalition forces. Fourteen heavily armed militants were killed.

Panetta called it "an intolerable situation."

The Afghan defense minister also said that Pakistan could do more, saying the Pakistanis are in a better position to provide intelligence or take law enforcement or military actions.

"I do hope that gradually they will come to the conclusion to cooperate with us," Wardak said. "If that cooperation starts, we will be able to disrupt their command and control, disrupt their training, disrupt their weapon recruitment and also will be able to eliminate or capture their leadership."

"Without doing that, I think our endeavor to achieve victory will become much more difficult," he said.

Panetta arrived in Afghanistan on Thursday to take stock of progress in the war and discuss plans for the troop drawdown, even as violence spiked in the south.

Making his fourth trip to the war zone as defense secretary, Panetta acknowledged the increase in attacks and that the insurgents appear to be much more organized. But he insisted that the overall level of violence was down.

Panetta said he wants to get an assessment of the situation from the top U.S. commander, Marine Gen. John Allen, and see how confident he is about NATO's ability to confront the threats both from the Taliban and the Haqqani network.

"I think it's important to make sure we are aware of the kind of attacks they're going to engage in ... as we go through the rest of the summer," Panetta told reporters traveling with him during a stop in New Delhi, India, on Wednesday.

Panetta spoke to troops gathered at the airport in Kabul just a day after three suicide attackers blew themselves up in a marketplace in southern Afghanistan, killing 22 people and wounding at least 50 others. In the east, meanwhile, Afghan officials and residents said a pre-dawn NATO airstrike targeting militants killed civilians celebrating a wedding, including women and children. A NATO forces spokesman said the coalition had no reports of civilians being killed in a raid, but was investigating the allegations of civilian casualties.

Allen has to withdraw 23,000 American troops by the end of September, leaving about 68,000 U.S. military personnel in the country. Once the 23,000 U.S. troops depart, Allen is expected to review how the fighting season is going and then will begin to put together an analysis for President Barack Obama on how troop withdrawals will proceed next year.

The defense secretary joked with the troops in Kabul about the U.S. strike that killed an al-Qaida leader Monday, saying, "the worst job you can get these days is to be a deputy leader in al-Qaida, or for that matter a leader."